1. Field of the Invention
The present invention relates to the technical field of fingerprint identification and, more particularly, to a combinational sensing type fingerprint identification device and method.
2. Description of Related Art
Biological feature sensing and comparing technologies have been maturely and widely applied in identifying and verifying the identity of a person. Typical biometric identification types include fingerprint, voiceprint, iris, retina identifications, and the like.
For consideration of safe, comfortable, and efficient identification, the fingerprint identification has become the most popular one. The fingerprint identification generally requires a scanning to input a fingerprint or a finger image of a user and store the unique features of the finger image and/or the fingerprint for being further compared with the fingerprint reference data built in a database so as to identify or verify the identity of a person.
The image input types of the fingerprint identification include optical scanning, thermal image sensing, capacitive sensing, and the like. The optical scanning type is difficult to be applied in a mobile electronic device due to its large volume, and the thermal image sensing type is not popular due to its poor accuracy and reliability. Thus, the capacitive sensing type gradually becomes the most important biometric identification technology for the mobile electronic device.
FIGS. 1A and 1B are local cross-sectional views of a typical fingerprint sensing region, which illustrate a capacitive fingerprint identification sensor interacting with a fingerprint. In FIG. 1A, the fingerprint has the ridges located on sensing elements. In FIG. 1B, the fingerprint has the ridges located on the gaps between the sensing elements.
As shown in FIGS. 1A and 1B, the capacitive finger identification sensor has a plurality of sensing elements 110, and the fingerprint 130 presses on a non-conductive substrate 120. Typically, a ridge 140 of the fingerprint 130 has an effective width of about 200 μm to 300 μm, and accordingly a sensing element 110 has a width smaller than 200 μm. In FIG. 1A, when the ridge 140 of the fingerprint 130 is located on the sensing element 110, a strong signal can be sensed, so that the sensed image of the fingerprint 130 can be effectively detected and accurately obtained. The ridge 140 of the fingerprint 130 in FIG. 1B is located between the sensing elements 110; that is, a valley 150 of the fingerprint 130 is located on a sensing element 110, resulting in that there is a weak signal or even no signal sensed. The two cases cited above are the extreme condition on fingerprint identification. However, when a sensing element 110 corresponds to a partial ridge 140 and a partial valley 150, the signal sensed by the sensing signal is in-between the above two extreme states, which is likely to be affected by noises, resulting in an erroneous decision. A direct approach to overcome this problem is to reduce the area of the sensing element for increasing the resolution. However, the increase of resolution may cause the difficulties in increasing the number of sensing elements and decreasing the amount of sensing, resulting in that the processing time is increased, and the accuracy of fingerprint identification is reduced.
Therefore, it is desirable to provide an improved fingerprint identification device and method to mitigate and/or obviate the aforementioned problems.